LED filament light bulb having different surface roughness filament base layer

ABSTRACT

An LED light bulb, comprising:a lamp housing, doped with a golden yellow material or coated with a yellow film on its surface,a bulb base, connected with the lamp housing, a stem with a stand extending to the center of the lamp housing, disposed in the lamp housing, a LED filament disposed in the lamp housing, at least a half of the LED filament is around a center axle of the LED light bulb, where the center axle of the LED light bulb is coaxial with the axle of the stand, two conductive supports, connected with the stem and the LED filament.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/234,124 filed on Dec. 27, 2018, which claims priority to ChinesePatent Applications No. 201510502630.3 filed on Aug. 27, 2015; No.201510966906.3 filed on Dec. 19, 2015; No. 201610041667.5 filed on Jan.22, 2016; No. 201610272153.0 filed on Apr. 27, 2016; No. 201610394610.3filed on Jun. 3, 2016; No. 201610586388.7 filed on Jul. 22, 2016; No.201610544049.2 filed on Jul. 7, 2016; No. 201610936171.4 filed on Nov.1, 2016; No. 201611108722.4 filed on Dec. 6, 2016; No. 201610281600.9filed on Apr. 29, 2016; No. 201710024877.8 filed on Jan. 13, 2017; No.201710079423.0 filed on Feb. 14, 2017; No. 201710138009.2 filed on Mar.9, 2017; No. 201710180574.5 filed on Mar. 23, 2017; No. 201710234618.8filed on Apr. 11, 2017; No. 201410510593.6 filed on Sep. 28, 2014; No.201510053077.X filed on Feb. 2, 2015; No. 201510316656.9 filed on Jun.10, 2015; No. 201510347410.8 filed on Jun. 19, 2015; No. 201510489363.0filed on Aug. 7, 2015; No. 201510555889.4 filed on Sep. 2, 2015; No.201710316641.1 filed on May 8, 2017; No. 201710839083.7 filed on Sep.18, 2017; No. 201710883625.0 filed on Sep. 26, 2017; No. 201730450712.8filed on Sep. 21, 2017; No. 201730453239.9 filed on Sep. 22, 2017; No.201730453237.X filed on Sep. 22, 2017; No. 201730537542.7 filed on Nov.3, 2017; No. 201730537544.6 filed on Nov. 3, 2017; No. 201730520672.Xfiled on Oct. 30, 2017; No. 201730517887.6 filed on Oct. 27, 2017; No.201730489929.X filed on Oct. 16, 2017; No. 201711434993.3 filed on Dec.26, 2017; No. 201711477767.3 filed on Dec. 29, 2017; No. 201810031786.1filed on Jan. 12, 2018; No. 201810065369.9 filed on Jan. 23, 2018; No.201810343825.1 filed on Apr. 17, 2018; No. 201810344630.9 filed on Apr.17, 2018; No. 201810501350.4 filed on May 23, 2018; No. 201810498980.0filed on May 23, 2018; No. 201810573314.9 filed on Jun. 6, 2018; No.201810836433.9 filed on Jul. 26, 2018; No. 201810943054.X filed on Aug.17, 2018; No. 201811005536.7 filed on Aug. 30, 2018; No. 201811005145.5filed on Aug. 30, 2018; No. 201811079889.1 filed on Sep. 17, 2018; No.201811277980.4 filed on Oct. 30, 2018; No. 201811285657.1 filed on Oct.31, 2018; No. 201811378173.1 filed on Nov. 19, 2018; No. 201811378189.2filed on Nov. 19, 2018; No. 201811549205.X filed on Dec. 18, 2018, eachof which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a lighting field, and moreparticularly to an LED filament light bulb having different surfaceroughness filament base layer.

RELATED ART

Incandescent bulbs have been widely used for homes or commerciallighting for decades. However, incandescent bulbs are generally withlower efficiency in terms of energy application, and about 90% of energyinput can be converted into a heat form to dissipate. In addition,because the incandescent bulb has a very limited lifespan (about 1,000hours), it needs to be frequently replaced. These traditionalincandescent bulbs are gradually replaced by other more efficientlighting devices, such as fluorescent lights, high-intensity dischargelamps, light-emitting diodes (LEDs) lights and the like. In theseelectric lamps, the LED light lamp attracts widespread attention in itslighting technology. The LED light lamp has the advantages of longlifespan, small in size, environmental protection and the like,therefore the application of the LED light lamp continuously grows.

In recent years, LED light bulbs with LED filaments have been providedon the market. At present, LED light bulbs using LED filaments asillumination sources still have the following problems to be improved.

Firstly, an LED hard filament is provided with a substrate (for example,a glass substrate) and a plurality of LED chips disposed on thesubstrate. However, the illumination appearance of the LED light bulbsrelies on multiple combinations of the LED hard filaments to produce thebetter illumination appearances. The illumination appearance of thesingle LED hard filament cannot meet the general needs in the market. Atraditional incandescent light bulb is provided with a tungstenfilament, the uniform light emitting can be generated due to the naturalbendable property of the tungsten filament. In contrast, the LED hardfilament is difficult to achieve such uniform illumination appearances.There are many reasons why LED hard filaments are difficult to achievethe uniform illumination appearance. In addition to the aforementionedlower bendable property, one of the reasons is that the substrate blocksthe light emitted by the LED chip, and furthermore the light generatedby the LED chip is displayed similar to a point light source whichcauses the light showing concentrated illumination and with poorillumination uniformity. In other words, a uniform distribution of thelight emitted from LED chip produces a uniform illumination appearanceof the LED filament. On the other hand, the light ray distributionsimilar to a point light source may result in uneven and concentratedillumination.

Secondly, there is one kind of LED soft filament, which is similar tothe structure of the above-mentioned LED hard filament and is employed aflexible printed circuit substrate (hereinafter referred to FPC) insteadof the glass substrate to enable the LED filament having a certaindegree of bending. However, by utilizing the LED soft filament made ofthe FPC, the FPC has a thermal expansion coefficient different from thatof the silicon gel coated covering the LED soft filament, and thelong-term use causes the displacement or even degumming of the LEDchips. Moreover, the FPC may not beneficial to flexible adjustment ofthe process conditions and the like. Besides, during bending the LEDsoft filament it has a challenge in the stability of the metal wirebonded between LED chips. When the arrangement of the LED chips in theLED soft filament is dense, if the adjacent LED chips are connected bymeans of metal wire bonding, it is easy to cause the stress to beconcentrated on a specific part of the LED soft filament when the LEDsoft filament is bent, thereby the metal wire bonding between the LEDchips are damaged and even broken.

In addition, the LED filament is generally disposed inside the LED lightbulb, and in order to present the aesthetic appearance and also to makethe illumination of the LED filament more uniform and widespread, theLED filament is bent to exhibit a plurality of curves. Since the LEDchips are arranged in the LED filaments, and the LED chips arerelatively hard objects, it is difficult for the LED filaments to bebent into a desired shape. Moreover, the LED filament is also prone tocracks due to stress concentration during bending. Publication No.CN204289439U discloses an LED filament with omni-directional lightcomprising a substrate mixed with phosphors, at least one electrodedisposed on the substrate, at least one LED chip mounted on thesubstrate, and the encapsulant coated on the LED chip. The substrateformed by the silicone resin contained with phosphors eliminates thecost of glass or sapphire as a substrate, and the LED filament equippingwith this kind of substrate avoids the influence of glass or sapphire onthe light emitting of the LED chip. The 360-degree light emitting isrealized, and the illumination uniformity and the light efficiency aregreatly improved. However, due to the fact that the substrate is formedby silicon resin, the defect of poor heat resistance is a disadvantage.

SUMMARY

It is noted that the present disclosure includes one or more inventivesolutions currently claimed or not claimed, and in order to avoidconfusion between the illustration of these embodiments in thespecification, a number of possible inventive aspects herein may becollectively referred to “present/the invention.”

A number of embodiments are described herein with respect to “theinvention.” However, the word “the invention” is used merely to describecertain embodiments disclosed in this specification, whether or not inthe claims, is not a complete description of all possible embodiments.Some embodiments of various features or aspects described below as “theinvention” may be combined in various ways to form an LED light bulb ora portion thereof. In accordance with another embodiment of the presentinvention, an LED filament comprises at least one LED section, aconductive section, at least two conductive electrodes and a lightconversion layer. The conductive section is located between two adjacentLED sections. The two conductive electrodes are disposed on the LEDfilament correspondingly and electrically connected to each of the LEDsections. The adjacent two LED sections are electrically connected toeach other through the conductive section. Each of the LED sectionsincludes at least two LED chips, and the LED chips are electricallyconnected to each other by at least one wire. The light conversion layercovers the LED sections, the conductive sections and the conductiveelectrodes, and a part of each of the two electrodes is exposedrespectively.

In accordance with an embodiment of the present invention, theconductive section includes a conductor connecting with the LED section,and the length of the wire connecting between the LED chips is less thanthe length of the conductor.

In accordance with an embodiment of the present invention, the lightconversion layer includes at least one top layer and one base layer.

In accordance with another embodiment of the present invention providesa composition which is suitable for use as a filament substrate or alight conversion layer, wherein the composition comprises at least amain material, a modifier and an additive. The main material is anorganosilicon-modified polyimide; the modifier is a thermal curingagent; and the additives comprise microparticles added into the mainmaterial, which may comprise phosphor particles, heat dispersingparticles. The additive also comprises a coupling agent.

The present disclosure provides a composition which is suitable for useas a filament substrate or a light-conversion layer, wherein the mainmaterial in the composition is an organosilicon-modified polyimide, i.e.a polyimide comprising a siloxane moiety, wherein theorganosilicon-modified polyimide comprises a repeating unit representedby the general Formula (I):

In general Formula (I), Ar¹ is a tetra-valent organic group having abenzene ring or an alicyclic hydrocarbon structure, Ar² is a di-valentorganic group, R is each independently methyl or phenyl, and n is 1˜5.

To make the above and other objects, features, and advantages of thepresent invention clearer and easier to understand, the followingembodiments will be described in detail with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent to thoseordinarily skilled in the art after reviewing the following detaileddescription and accompanying drawings, in which:

FIG. 1 is a cross sectional view of an LED filament in accordance withan embodiment of the present invention;

FIG. 2 shows the particle size distributions of the heat dispersingparticles with different specifications;

FIG. 3A shows the SEM image of an organosilicon-modified polyimide resincomposition composite film (substrate);

FIG. 3B shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according to anembodiment of the present invention;

FIG. 3C shows the cross-sectional scheme of an organosilicon-modifiedpolyimide resin composition composite film (substrate) according toanother embodiment of the present disclosure;

FIG. 4A illustrates a perspective view of an LED light bulb according toan embodiment of the instant disclosure;

FIG. 4B is a projection of a top view of an LED filament of the LEDlight bulb of FIG. 4A;

FIGS. 5A to 5D are respectively a perspective view, a side view, anotherside view and a top view of an LED light bulb in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

The present disclosure provides a novel LED filament and its applicationthe LED light bulb. The present disclosure will now be described in thefollowing embodiments with reference to the drawings. The followingdescriptions of various implementations are presented herein for purposeof illustration and giving examples only. This invention is not intendedto be exhaustive or to be limited to the precise form disclosed. Theseexample embodiments are just that examples and many implementations andvariations are possible that do not require the details provided herein.It should also be emphasized that the disclosure provides details ofalternative examples, but such listing of alternatives is notexhaustive. Furthermore, any consistency of detail between variousexamples should not be interpreted as requiring such detail it isimpracticable to list every possible variation for every featuredescribed herein. The language of the claims should be referenced indetermining the requirements of the invention.

In the drawings, the size and relative sizes of components may beexaggerated for clarity. Like numbers refer to like elements throughout.

Terms such as “about” or “approximately” may reflect sizes,orientations, or layouts that vary only in a small relative manner,and/or in a way that does not significantly alter the operation,functionality, or structure of certain elements. For example, a rangefrom “about 0.1 to about 1” may encompass a range such as a 0%-5%deviation around 0.1 and a 0% to 5% deviation around 1, especially ifsuch deviation maintains the same effect as the listed range.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent application, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

The connection mode between the conductor in the conductive section andthe light conversion layer is described as follows. Referring to FIG. 1,in the LED filament structure shown in FIG. 1, the LED filament 400 hasa light conversion layer 420, the LED sections 402, 404, the conductiveelectrodes 410, 412, and at least one conductive section 430. Theconductive section 430 is located between adjacent LED sections 402 and404. The LED sections 402 and 404 include at least two LED chips 442electrically connected to each other through the wires 440. In thepresent embodiment, the conductive section 430 includes a conductor 430a. The conductive section 430 and the LED sections 402, 404 areelectrically connected by wires 450, that is, two LED chips respectivelylocated in the adjacent two LED sections 402, 404 and closest to theconductive section 430 are electrically connected to each other throughthe wires 450 connecting with the conductor 430 a in the conductivesection 430. The length of the conductive section 430 is greater thanthe distance between two adjacent LED chips in one single LED sections402, 404, and the length of the wire 440 is less than the length of theconductor 430 a. The light conversion layer 420 is disposed on at leastone side of the LED chip 442 and the conductive electrode 410, 412, anda part of the two conductive electrodes is exposed from the lightconversion layer. The light conversion layer 420 includes at least a toplayer 420 a and a base layer 420 b. In the present embodiment, the LEDsections 402, 404, the conductive electrodes 410, 412, and theconductive section 430 are all attached to the base layer 420 b.

The conductor 430 a can be a copper foil or other electricallyconductive material, and the conductor 430 a has opening. The uppersurface of the conductor 430 a may further have a silver plating layer,and subsequently, the LED chip 442 may be attached to the base layer 420b by means of die bond paste or the like. Thereafter, a phosphor glue orphosphor film is applied to coat over the LED chip 442, the wires 440,450, and a portion of the conductive electrodes 410, 412 to form a lightconversion layer 420. The width or/and the length of the opening of theconductor 430 a are respectively larger than the width or/and the lengthof the LED chip 442 and defining the position of the LED chip 442. Atleast two of the six faces of the LED chip, generally five faces in thepresent embodiment, being covered by the phosphor glue. The wires 440,450 may be gold wires.

According to the aforementioned embodiments of the present invention,since the LED filament structure is provided with at least one LEDsection and at least one conductive section, when the LED filament isbent, the stress is easily concentrated on the conductive section.Therefore, the breakage probability of the gold wire connected betweenthe adjacent LED chips is reduced during bending. Thereby, the qualityof the LED filament and its application is improved. The conductor inthe LED filament conductive section may be in a shape of “M” or waveprofile for providing better flexibility in extending of the LEDfilament.

The next part will describe the material of the filament of the presentinvention. The material suitable for manufacturing a filament substrateor a light-conversion layer for LED should have properties such asexcellent light transmission, good heat resistance, excellent thermalconductivity, appropriate refraction rate, excellent mechanicalproperties and good warpage resistance. All the above properties can beachieved by adjusting the type and the content of the main material, themodifier and the additive contained in the organosilicon-modifiedpolyimide composition. The present disclosure provides a filamentsubstrate or a light-conversion layer formed from a compositioncomprising an organosilicon-modified polyimide. The composition can meetthe requirements on the above properties. In addition, the type and thecontent of one or more of the main material, the modifier (thermalcuring agent) and the additive in the composition can be modified toadjust the properties of the filament substrate or the light-conversionlayer, so as to meet special environmental requirements. Themodification of each property is described herein below.

Adjustment of the Organosilicon-Modified Polyimide

The organosilicon-modified polyimide provided herein comprises arepeating unit represented by the following general Formula (I):

In general Formula (I), Ar¹ is a tetra-valent organic group. The organicgroup has a benzene ring or an alicyclic hydrocarbon structure. Thealicyclic hydrocarbon structure may be monocyclic alicyclic hydrocarbonstructure or a bridged-ring alicyclic hydrocarbon structure, which maybe a dicyclic alicyclic hydrocarbon structure or a tricyclic alicyclichydrocarbon structure. The organic group may also be a benzene ring oran alicyclic hydrocarbon structure comprising a functional group havingactive hydrogen, wherein the functional group having active hydrogen isone or more of hydroxyl, amino, carboxy, amido and mercapto.

Ar² is a di-valent organic group, which organic group may have forexample a monocyclic alicyclic hydrocarbon structure or a di-valentorganic group comprising a functional group having active hydrogen,wherein the functional group having active hydrogen is one or more ofhydroxyl, amino, carboxy, amido and mercapto.

R is each independently methyl or phenyl.

n is 1˜5, preferably 1, 2, 3 or 5.

The polymer of general Formula (I) has a number average molecular weightof 5000˜100000, preferably 10000˜60000, more preferably 20000˜40000. Thenumber average molecular weight is determined by gel permeationchromatography (GPC) and calculated based on a calibration curveobtained by using standard polystyrene. When the number averagemolecular weight is below 5000, a good mechanical property is hard to beobtained after curing, especially the elongation tends to decrease. Onthe other hand, when it exceeds 100000, the viscosity becomes too highand the resin is hard to be formed.

Ar¹ is a component derived from a dianhydride, which may be an aromaticanhydride or an aliphatic anhydride. The aromatic anhydride includes anaromatic anhydride comprising only a benzene ring, a fluorinatedaromatic anhydride, an aromatic anhydride comprising amido group, anaromatic anhydride comprising ester group, an aromatic anhydridecomprising ether group, an aromatic anhydride comprising sulfide group,an aromatic anhydride comprising sulfonyl group, and an aromaticanhydride comprising carbonyl group.

Examples of the aromatic anhydride comprising only a benzene ringinclude pyromellitic dianhydride (PMDA), 2,3,3′,4′-biphenyltetracarboxylic dianhydride (aBPDA), 3,3′,4,4′-biphenyl tetracarboxylicdianhydride (sBPDA), and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA). Examples of thefluorinated aromatic anhydride include4,4′-(hexafluoroisopropylidene)diphthalic anhydride which is referred toas 6FDA. Examples of the aromatic anhydride comprising amido groupinclude N,N′-(5,5′-(perfluoropropane-2,2-diyl)bis(2-hydroxy-5,1-phenylene))bis(1,3-dioxo-1,3-dihydroisobenzofuran)-5-arboxamide) (6FAP-ATA), andN,N′-(9H-fluoren-9-ylidenedi-4,1-phenylene)bis[1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxamide] (FDA-ATA). Examples of the aromatic anhydride comprisingester group include p-phenylene bis(trimellitate) dianhydride (TAHQ).Examples of the aromatic anhydride comprising ether group include4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA),4,4′-oxydiphthalic dianhydride (sODPA), 2,3,3′,4′-diphenyl ethertetracarboxylic dianhydride (aODPA), and4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride (BPADA).Examples of the aromatic anhydride comprising sulfide group include4,4′-bis(phthalic anhydride)sulfide (TPDA). Examples of the aromaticanhydride comprising sulfonyl group include3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA). Examples ofthe aromatic anhydride comprising carbonyl group include3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA).

The alicyclic anhydride includes 1,2,4,5-cyclohexanetetracarboxylic aciddianhydride which is referred to as HPMDA, 1,2,3,4-butanetetracarboxylicdianhydride (BDA),tetrahydro-1H-5,9-methanopyrano[3,4-d]oxepine-1,3,6,8(4H)-tetrone (TCA),hexahydro-4,8-ethano-1H,3H-benzo [1,2-C:4,5-C′]difuran-1,3,5,7-tetrone(BODA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), and1,2,3,4-cyclopentanetetracarboxylic dianhydride (CpDA); or alicyclicanhydride comprising an olefin structure, such asbicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (COeDA).When an anhydride comprising ethynyl such as4,4′-(ethyne-1,2-diyl)diphthalic anhydride (EBPA) is used, themechanical strength of the light-conversion layer can be further ensuredby post-curing.

Considering the solubility, 4,4′-oxydiphthalic anhydride (sODPA),3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA),cyclobutanetetracarboxylic dianhydride (CBDA) and4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) arepreferred. The above dianhydride can be used alone or in combination.

Ar² is derived from diamine which may be an aromatic diamine or analiphatic diamine. The aromatic diamine includes an aromatic diaminecomprising only a benzene ring, a fluorinated aromatic diamine, anaromatic diamine comprising ester group, an aromatic diamine comprisingether group, an aromatic diamine comprising amido group, an aromaticdiamine comprising carbonyl group, an aromatic diamine comprisinghydroxyl group, an aromatic diamine comprising carboxy group, anaromatic diamine comprising sulfonyl group, and an aromatic diaminecomprising sulfide group.

The aromatic diamine comprising only a benzene ring includesm-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,2,6-diamino-3,5-diethyltoluene, 3,3′-dimethylbiphenyl-4,4′-diamine9,9-bis(4-aminophenyl)fluorene (FDA),9,9-bis(4-amino-3-methylphenyl)fluorene, 2,2-bis(4-aminophenyl)propane,2,2-bis(3-methyl-4-aminophenyl)propane,4,4′-diamino-2,2′-dimethylbiphenyl (APB). The fluorinated aromaticdiamine includes 2,2′-bis(trifluoromethyl)benzidine (TFMB),2,2-bis(4-aminophenyl)hexafluoropropane (6FDAM),2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), and2,2-bis(3-amino-4-methylphenyl)hexafluoropropane (BIS-AF-AF). Thearomatic diamine comprising ester group includes[4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate (ABHQ),bis(4-aminophenyl)terephthalate (BPTP), and 4-aminophenyl4-aminobenzoate (APAB). The aromatic diamine comprising ether groupincludes 2,2-bis[4-(4-aminophenoxy)phenyl]propane) (BAPP),2,2′-bis[4-(4-aminophenoxy)phenyl]propane (ET-BDM),2,7-bis(4-aminophenoxy)-naphthalene (ET-2,7-Na),1,3-bis(3-aminophenoxy)benzene (TPE-M),4,4′-[1,4-phenyldi(oxy)]bis[3-(trifluoromethyl)aniline] (p-6FAPB),3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether (ODA),1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene(TPE-Q), and 4,4′-bis(4-aminophenoxy)biphenyl (BAPB). The aromaticdiamine comprising amido group includesN,N′-bis(4-aminophenyl)benzene-1,4-dicarboxamide (BPTPA), 3,4′-diaminobenzanilide (m-APABA), and 4,4′-diaminobenzanilide (DABA). The aromaticdiamine comprising carbonyl group includes 4,4′-diaminobenzophenone(4,4′-DABP), and bis(4-amino-3-carboxyphenyl) methane (or referred to as6,6′-diamino-3,3′-methylanediyl-dibenzoic acid). The aromatic diaminecomprising hydroxyl group includes 3,3′-dihydroxybenzidine (HAB), and2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). The aromaticdiamine comprising carboxy group includes6,6′-diamino-3,3′-methylanediyl-dibenzoic acid (MBAA), and3,5-diaminobenzoic acid (DBA). The aromatic diamine comprising sulfonylgroup includes 3,3′-diaminodiphenyl sulfone (DDS),4,4′-diaminodiphenylsulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) (or referred to as4,4′-bis(4-aminophenoxy)diphenylsulfone), and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). The aromatic diaminecomprising sulfide group includes 4,4′-diaminodiphenyl sulfide.

The aliphatic diamine is a diamine which does not comprise any aromaticstructure (e.g., benzene ring). The aliphatic diamine includesmonocyclic alicyclic amine and straight chain aliphatic diamine, whereinthe straight chain aliphatic diamine include siloxane diamine, straightchain alkyl diamine and straight chain aliphatic diamine comprisingether group. The monocyclic alicyclic diamine includes4,4′-diaminodicyclohexylmethane (PACM), and3,3′-dimethyl-4,4-diaminodicyclohexylmethane (DMDC). The siloxanediamine (or referred to as amino-modified silicone) includesα,ω-(3-aminopropyl)polysiloxane (KF8010), X22-161A, X22-161B, NH15D, and1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (PAME). Thestraight chain alkyl diamine has 6˜12 carbon atoms, and is preferablyun-substituted straight chain alkyl diamine. The straight chainaliphatic diamine comprising ether group includes ethylene glycoldi(3-aminopropyl) ether.

The diamine can also be a diamine comprising fluorenyl group. Thefluorenyl group has a bulky free volume and rigid fused-ring structure,which renders the polyimide good heat resistance, thermal and oxidationstabilities, mechanical properties, optical transparency and goodsolubility in organic solvents. The diamine comprising fluorenyl group,such as 9,9-bis(3,5-difluoro-4-aminophenyl)fluorene, may be obtainedthrough a reaction between 9-fluorenone and 2,6-dichloroaniline. Thefluorinated diamine can be1,4-bis(3′-amino-5′-trifluoromethylphenoxy)biphenyl, which is ameta-substituted fluorine-containing diamine having a rigid biphenylstructure. The meta-substituted structure can hinder the charge flowalong the molecular chain and reduce the intermolecular conjugation,thereby reducing the absorption of visible lights. Using asymmetricdiamine or anhydride can increase to some extent the transparency of theorganosilicon-modified polyimide resin composition. The above diaminescan be used alone or in combination.

Examples of diamines having active hydrogen include diamines comprisinghydroxyl group, such as 3,3′-diamino-4,4′-dihydroxybiphenyl,4,4′-diamino-3,3′-dihydroxy-1,1′-biphenyl (or referred to as3,3′-dihydroxybenzidine) (HAB), 2,2-bis(3-amino-4-hydroxyphenyl)propane(BAP), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP),1,3-bis(3-hydro-4-aminophenoxy) benzene,1,4-bis(3-hydroxy-4-aminophenyl)benzene and3,3′-diamino-4,4′-dihydroxydiphenyl sulfone (ABPS). Examples of diaminescomprising carboxy group include 3,5-diaminobenzoic acid,bis(4-amino-3-carboxyphenyl)methane (or referred to as6,6′-diamino-3,3′-methylenedibenzoic acid),3,5-bis(4-aminophenoxy)benzoic acid, and1,3-bis(4-amino-2-carboxyphenoxy)benzene. Examples of diaminescomprising amino group include 4,4′-diaminobenzanilide (DABA),2-(4-aminophenyl)-5-aminobenzoimidazole, diethylenetriamine,3,3′-diaminod ipropylamine, triethylenetetramine, andN,N′-bis(3-aminopropyl)ethylenediamine (or referred to asN,N-di(3-aminopropyl)ethylethylamine). Examples of diamines comprisingthiol group include 3,4-diaminobenzenethiol. The above diamines can beused alone or in combination.

Polyimide can be obtained by carrying out an equilibrium reaction togive a poly(amic acid) which is heated to dehydrate. In otherembodiments, the polyimide backbone may have a small amount of amicacid. For example, the ratio of amic acid to imide in the polyimidemolecule may be 1˜3:100. Due to the interaction between amic acid andthe epoxy resin, the substrate has superior properties. In otherembodiments, a solid state material such as a thermal curing agent,inorganic heat dispersing particles and phosphor can also be added atthe state of poly(amic acid) to give the substrate. In addition,solubilized polyimide can also be obtained by direct heating anddehydration after mixing of alicylic anhydride and diamine. Suchsolubilized polyimide, as an adhesive material, has a good lighttransmittance. In addition, it is liquid state; therefore, other solidmaterials (such as the inorganic heat dispersing particles and thephosphor) can be dispersed in the adhesive material more sufficiently.

In one embodiment for preparing the organosilicon-modified polyimide,the organosilicon-modified polyimide can be produced by dissolving thepolyimide obtained by heating and dehydration after mixing a diamine andan anhydride and a siloxane diamine in a solvent. In another embodiment,the amidic acid, before converting to polyimide, is reacted with thesiloxane diamine.

The molar ratio of dianhydride to diamine may be 1:1. The molarpercentage of the diamine comprising a functional group having activehydrogen may be 5˜25% of the total amount of diamine. The temperatureunder which the polyimide is synthesized is preferably 80˜250° C., morepreferably 100˜200° C. The reaction time may vary depending on the sizeof the batch. For example, the reaction time for obtaining 10˜30 gpolyimide is 6˜10 hours.

The organosilicon-modified polyimide can be classified as fluorinatedaromatic organosilicon-modified polyimides and aliphaticorganosilicon-modified polyimides. The fluorinated aromaticorganosilicon-modified polyimides are synthesized from siloxane-typediamine, aromatic diamine comprising fluoro (F) group (or referred to asfluorinated aromatic diamine) and aromatic dianhydride comprising fluoro(F) group (or referred to as fluorinated aromatic anhydride). Thealiphatic organosilicon-modified polyimides are synthesized fromdianhydride, siloxane-type diamine and at least one diamine notcomprising aromatic structure (e.g., benzene ring) (or referred to asaliphatic diamine), or from diamine (one of which is siloxane-typediamine) and at least one dianhydride not comprising aromatic structure(e.g., benzene ring) (or referred to as aliphatic anhydride). Thealiphatic organosilicon-modified polyimide includes semi-aliphaticorganosilicon-modified polyimide and fully aliphaticorganosilicon-modified polyimide. The fully aliphaticorganosilicon-modified polyimide is synthesized from at least onealiphatic dianhydride, siloxane-type diamine and at least one aliphaticdiamine. The raw materials for synthesizing the semi-aliphaticorganosilicon-modified polyimide include at least one aliphaticdianhydride or aliphatic diamine. The raw materials required forsynthesizing the organosilicon-modified polyimide and the siloxanecontent in the organosilicon-modified polyimide would have certaineffects on transparency, chromism, mechanical property, warpage extentand refractivity of the substrate.

The organosilicon-modified polyimide of the present disclosure has asiloxane content of 20˜75 wt %, preferably 30˜70 wt %, and a glasstransition temperature of below 150° C. The glass transition temperature(Tg) is determined on TMA-60 manufactured by Shimadzu Corporation afteradding a thermal curing agent to the organosilicon-modified polyimide.The determination conditions include: load: 5 gram; heating rate: 10°C./min; determination environment: nitrogen atmosphere; nitrogen flowrate: 20 ml/min; temperature range: −40 to 300° C. When the siloxanecontent is below 20%, the film prepared from the organosilicon-modifiedpolyimide resin composition may become very hard and brittle due to thefilling of the phosphor and thermal conductive fillers, and tend to warpafter drying and curing, and therefore has a low processability. Inaddition, its resistance to thermochromism becomes lower. On the otherhand, when the siloxane content is above 75%, the film prepared from theorganosilicon-modified polyimide resin composition becomes opaque, andhas reduced transparency and tensile strength. Here, the siloxanecontent is the weight ratio of siloxane-type diamine(having a structureshown in Formula (A)) to the organosilicon-modified polyimide, whereinthe weight of the organosilicon-modified polyimide is the total weightof the diamine and the dianhydride used for synthesizing theorganosilicon-modified polyimide subtracted by the weight of waterproduced during the synthesis.

Wherein R is methyl or phenyl, preferably methyl, n is 1˜5, preferably1, 2, 3 or 5.

The only requirements on the organic solvent used for synthesizing theorganosilicon-modified polyimide are to dissolve theorganosilicon-modified polyimide and to ensure the affinity(wettability) to the phosphor or the fillers to be added. However,excessive residue of the solvent in the product should be avoided.Normally, the number of moles of the solvent is equal to that of waterproduced by the reaction between diamine and anhydride. For example, 1mol diamine reacts with 1 mol anhydride to give 1 mol water; then theamount of solvent is 1 mol. In addition, the organic solvent used has aboiling point of above 80° C. and below 300° C., more preferably above120° C. and below 250° C., under standard atmospheric pressure. Sincedrying and curing under a lower temperature are needed after coating, ifthe temperature is lower than 120° C., good coating cannot be achieveddue to high drying speed during the coating process. If the boilingpoint of the organic solvent is higher than 250° C., the drying under alower temperature may be deferred. Specifically, the organic solvent maybe an ether-type organic solvent, an ester-type organic solvent, adimethyl ether-type organic solvent, a ketone-type organic solvent, analcohol-type organic solvent, an aromatic hydrocarbon solvent or othersolvents. The ether-type organic solvent includes ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, propylene glycolmonomethyl ether, propylene glycol monoethyl ether, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutylether, diethylene glycol dimethyl ether, diethylene glycol diethylether, diethylene glycol methyl ethyl ether, dipropylene glycol dimethylether or diethylene glycol dibutyl ether, and diethylene glycol butylmethyl ether. The ester-type organic solvent includes acetates,including ethylene glycol monoethyl ether acetate, diethylene glycolmonobutyl ether acetate, propylene glycol monomethyl ether acetate,propyl acetate, propylene glycol diacetate, butyl acetate, isobutylacetate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, benzylacetate and 2-(2-butoxyethoxy)ethyl acetate; and methyl lactate, ethyllactate, n-butyl acetate, methyl benzoate and ethyl benzoate. Thedimethyl ether-type solvent includes triethylene glycol dimethyl etherand tetraethylene glycol dimethyl ether. The ketone-type solventincludes acetylacetone, methyl propyl ketone, methyl butyl ketone,methyl isobutyl ketone, cyclopentanone, and 2-heptanone. Thealcohol-type solvent includes butanol, isobutanol, isopentanol,4-methyl-2-pentano1,3-methyl-2-butanol, 3-methyl-3-methoxybutanol, anddiacetone alcohol. The aromatic hydrocarbon solvent includes toluene andxylene. Other solvents include γ-butyrolactone, N-methylpyrrolidone,N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

The present disclosure provides an organosilicon-modified polyimideresin composition comprising the above organosilicon-modified polyimideand a thermal curing agent, which may be epoxy resin, hydrogenisocyanate or bisoxazoline compound. In one embodiment, based on theweight of the organosilicon-modified polyimide, the amount of thethermal curing agent is 5˜12% of the weight of theorganosilicon-modified polyimide. The organosilicon-modified polyimideresin composition may further comprise heat dispersing particles andphosphor.

Light Transmittance

The factors affecting the light transmittance of theorganosilicon-modified polyimide resin composition at least include thetype of the main material, the type of the modifier(thermal curingagent), the type and content of the heat dispersing particles, and thesiloxane content. Light transmittance refers to the transmittance of thelight near the main light-emitting wavelength range of the LED chip. Forexample, blue LED chip has a main light-emitting wavelength of around450 nm, then the composition or the polyimide should have low enough oreven no absorption to the light having a wavelength around 450 nm, so asto ensure that most or even all the light can pass through thecomposition or the polyimide. In addition, when the light emitted by theLED chip passes through the interface of two materials, the closer therefractive indexes of the two materials, the higher the light outputefficiency. In order to be close to the refractive index of the material(such as die bonding glue) contacting with the filament substrate (orbase layer), the organosilicon-modified polyimide composition has arefractive index of 1.4˜1.7, preferably 1.4˜1.55. In order to use theorganosilicon-modified polyimide resin composition as substrate in thefilament, the organosilicon-modified polyimide resin composition isrequired to have good light transmittance at the peak wavelength ofInGaN of the blue-excited white LED. In order to obtain a goodtransmittance, the raw materials for synthesizing theorganosilicon-modified polyimide, the thermal curing agent and the heatdispersing particles can be adjusted. Because the phosphor in theorganosilicon-modified polyimide resin composition may have certaineffect on the transmittance test, the organosilicon-modified polyimideresin composition used for the transmittance test does not comprisephosphor. Such an organosilicon-modified polyimide resin composition hasa transmittance of 86˜93%, preferably 88˜91%, or preferably 89˜92%, orpreferably 90˜93%.

In the reaction of anhydride and diamine to produce polyimide, theanhydride and the diamine may vary. In other words, the polyimidesproduced from different anhydrides and different diamines may havedifferent light transmittances. The aliphatic organosilicon-modifiedpolyimide resin composition comprises the aliphaticorganosilicon-modified polyimide and the thermal curing agent, while thefluorinated aromatic organosilicon-modified polyimide resin compositioncomprises the fluorinated aromatic organosilicon-modified polyimide andthe thermal curing agent. Since the aliphatic organosilicon-modifiedpolyimide has an alicyclic structure, the aliphaticorganosilicon-modified polyimide resin composition has a relatively highlight transmittance. In addition, the fluorinated aromatic,semi-aliphatic and full aliphatic polyimides all have good lighttransmittance in respect of the blue LED chips. The fluorinated aromaticorganosilicon-modified polyimide is synthesized from a siloxane-typediamine, an aromatic diamine comprising a fluoro (F) group (or referredto as fluorinated aromatic diamine) and an aromatic dianhydridecomprising a fluoro (F) group (or referred to as fluorinated aromaticanhydride). In other words, both Ar¹ and Ar² comprise a fluoro (F)group. The semi-aliphatic and full aliphatic organosilicon-modifiedpolyimides are synthesized from a dianhydride, a siloxane-type diamineand at least one diamine not comprising an aromatic structure (e.g. abenzene ring) (or referred to as aliphatic diamine), or from a diamine(one of the diamine is siloxane-type diamine) and at least onedianhydride not comprising an aromatic structure (e.g. a benzene ring)(or referred to as aliphatic anhydride). In other words, at least one ofAr¹ and Ar² has an alicyclic hydrocarbon structure.

Although blue LED chips have a main light-emitting wavelength of 450 nm,they may still emit a minor light having a shorter wavelength of around400 nm, due to the difference in the conditions during the manufactureof the chips and the effect of the environment. The fluorinatedaromatic, semi-aliphatic and full aliphatic polyimides have differentabsorptions to the light having a shorter wavelength of 400 nm. Thefluorinated aromatic polyimide has an absorbance of about 20% to thelight having a shorter wavelength of around 400 nm, i.e. the lighttransmittance of the light having a wavelength of 400 nm is about 80%after passing through the fluorinated aromatic polyimide. Thesemi-aliphatic and full aliphatic polyimides have even lower absorbanceto the light having a shorter wavelength of 400 nm than the fluorinatedaromatic polyimide, which is only 12%. Accordingly, in an embodiment, ifthe LED chips used in the LED filament have a uniform quality, and emitless blue light having a shorter wavelength, the fluorinated aromaticorganosilicon-modified polyimide may be used to produce the filamentsubstrate or the light-conversion layer. In another embodiment, if theLED chips used in the LED filament have different qualities, and emitmore blue light having a shorter wavelength, the semi-aliphatic or fullaliphatic organosilicon-modified polyimides may be used to produce thefilament substrate or the light-conversion layer.

Adding different thermal curing agents imposes different effects on thelight transmittance of the organosilicon-modified polyimide. Table 1-1shows the effect of the addition of different thermal curing agents onthe light transmittance of the full aliphatic organosilicon-modifiedpolyimide. At the main light-emitting wavelength of 450 nm for the blueLED chip, the addition of different thermal curing agents renders nosignificant difference to the light transmittance of the full aliphaticorganosilicon-modified polyimide; while at a short wavelength of 380 nm,the addition of different thermal curing agents does affect the lighttransmittance of the full aliphatic organosilicon-modified polyimide.The organosilicon-modified polyimide itself has a poorer transmittanceto the light having a short wavelength (380 nm) than to the light havinga long wavelength (450 nm). However, the extent of the difference varieswith the addition of different thermal curing agents. For example, whenthe thermal curing agent KF105 is added to the full aliphaticorganosilicon-modified polyimide, the extent of the reduction in thelight transmittance is less. In comparison, when the thermal curingagent 2021p is added to the full aliphatic organosilicon-modifiedpolyimide, the extent of the reduction in the light transmittance ismore. Accordingly, in an embodiment, if the LED chips used in the LEDfilament have a uniform quality, and emit less blue light having a shortwavelength, the thermal curing agent BPA or the thermal curing agent2021p may be added. In comparison, in an embodiment, if the LED chipsused in the LED filament have different qualities, and emit more bluelight having a short wavelength, the thermal curing agent KF105 may beused. Both Table 1-1 and Table 1-2 show the results obtained in thetransmittance test using Shimadzu UV-Vis Spectrometer UV-1800. The lighttransmittances at wavelengths 380 nm, 410 nm and 450 nm are tested basedon the light emission of white LEDs.

TABLE 1-1 Mechanical Thermal Curing Light Transmittance (%) StrengthOrganosilicon- Agent Film Tensile Modified Amount Thickness ElongationStrength Polyimides Types (%) 380 nm 410 nm 450 nm (μm) (%) (MPa) FullAliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic X22-163 8.086.6 88.6 90.2 44 43.4 8.0 Full Aliphatic KF105 8.0 87.2 88.9 90.4 4472.6 7.1 Full Aliphatic EHPE3150 8.0 87.1 88.9 90.5 44 40.9 13.1 FullAliphatic 2021p 8.0 86.1 88.1 90.1 44 61.3 12.9

TABLE 1-2 Thermal Light Transmittance (%) Mechanical StrengthOrganosilicon- Curing Agent Film Tensile Modified Amount ThicknessElongation Strength Polyimides Types (%) 380 nm 410 nm 450 nm (mm) (%)(MPa) Full Aliphatic BPA 4.0 86.2 88.4 89.7 44 22.5 9.8 Full Aliphatic8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic 12.0 87.3 88.9 90.5 4420.1 9.0

Even when the same thermal curing agent is added, different added amountthereof will have different effects on the light transmittance. Table1-2 shows that when the added amount of the thermal curing agent BPA tothe full aliphatic organosilicon-modified polyimide is increased from 4%to 8%, the light transmittance increases. However, when the added amountis further increased to 12%, the light transmittance keeps almostconstant. It is shown that the light transmittance increases with theincrease of the added amount of the thermal curing agent, but after thelight transmittance increases to certain degree, adding more thermalcuring agent will have limited effect on the light transmittance.

Different heat dispersing particles would have different transmittances.If heat dispersing particles with low light transmittance or low lightreflection are used, the light transmittance of theorganosilicon-modified polyimide resin composition will be lower. Theheat dispersing particles in the organosilicon-modified polyimide resincomposition of the present disclosure are preferably selected to betransparent powders or particles with high light transmittance or highlight reflection. Since the soft filament for the LED is mainly for thelight emission, the filament substrate should have good lighttransmittance. In addition, when two or more types of heat dispersingparticles are mixed, particles with high light transmittance and thosewith low light transmittance can be used in combination, wherein theproportion of particles with high light transmittance is higher thanthat of particles with low light transmittance. In an embodiment, forexample, the weight ratio of particles with high light transmittance toparticles with low light transmittance is 3˜5:1.

Different siloxane content also affects the light transmittance. As canbe seen from Table 2, when the siloxane content is only 37 wt %, thelight transmittance is only 85%. When the siloxane content is increasedto above 45%, the light transmittance exceeds 94%.

TABLE 2 Elongation Organosilicon- Siloxane Thermal Tensile Elastic atResistance Modified Content Curing Tg Strength Modulus Break Chemical toPolyimide (wt %) Agent (° C.) (MPa) (GPa) (%) Transmittance ResistanceThermochromism 1 37 BPA 158 33.2 1.7 10 85 Δ 83 2 41 BPA 142 38.0 1.4 1292 ∘ 90 3 45 BPA 145 24.2 1.1 15 97 Δ 90 4 64 BPA 30 8.9 0.04 232 94 ∘92 5 73 BPA 0 1.8 0.001 291 96 ∘ 95Heat Resistance

The factors affecting the heat resistance of the organosilicon-modifiedpolyimide resin composition include at least the type of the mainmaterial, the siloxane content, and the type and content of the modifier(thermal curing agent).

All the organosilicon-modified polyimide resin composition synthesizedfrom fluorinated aromatic, semi-aliphatic and, full aliphaticorganosilicon-modified polyimide have superior heat resistance, and aresuitable for producing the filament substrate or the light-conversionlayer. Detailed results from the accelerated heat resistance and agingtests (300° C.×1 hr) show that the fluorinated aromaticorganosilicon-modified polyimide has better heat resistance than thealiphatic organosilicon-modified polyimide. Accordingly, in anembodiment, if a high power, high brightness LED chip is used as the LEDfilament, the fluorinated aromatic organosilicon-modified polyimide maybe used to produce the filament substrate or the light-conversion layer.

The siloxane content in the organosilicon-modified polyimide will affectthe resistance to thermochromism of the organosilicon-modified polyimideresin composition. The resistance to thermochromism refers to thetransmittance determined at 460 nm after placing the sample at 200° C.for 24 hours. As can be seen from Table 2, when the siloxane content isonly 37 wt %, the light transmittance after 24 hours at 200° C. is only83%. As the siloxane content is increased, the light transmittance after24 hours at 200° C. increases gradually. When the siloxane content is 73wt %, the light transmittance after 24 hours at 200° C. is still as highas 95%. Accordingly, increasing the siloxane content can effectivelyincrease the resistance to thermochromism of the organosilicon-modifiedpolyimide.

In the cross-linking reaction between the organosilicon-modifiedpolyimide and the thermal curing agent, the thermal curing agent shouldhave an organic group which is capable of reacting with the functionalgroup having active hydrogen in the polyimide. The amount and the typeof the thermal curing agent have certain effects on chromism, mechanicalproperty and refractive index of the substrate. Accordingly, a thermalcuring agent with good heat resistance and transmittance can beselected. Examples of the thermal curing agent include epoxy resin,isocyanate, bismaleimide, and bisoxazoline compounds. The epoxy resinmay be bisphenol A epoxy resin, such as BPA; or siloxane-type epoxyresin, such as KF105, X22-163, and X22-163A; or alicylic epoxy resin,such as 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate(2021P), EHPE3150, and EHPE3150CE. Through the bridging reaction by theepoxy resin, a three dimensional bridge structure is formed between theorganosilicon-modified polyimide and the epoxy resin, increasing thestructural strength of the adhesive itself. In an embodiment, the amountof the thermal curing agent may be determined according to the molaramount of the thermal curing agent reacting with the functional grouphaving active hydrogen in theorganosilicon-modified polyimide. In anembodiment, the molar amount of the functional group having activehydrogen reacting with the thermal curing agent is equal to that of thethermal curing agent. For example, when the molar amount of thefunctional group having active hydrogen reacting with the thermal curingagent is 1 mol, the molar amount of the thermal curing agent is 1 mol.

Thermal Conductivity

The factors affecting the thermal conductivity of theorganosilicon-modified polyimide resin composition include at least thetype and content of the phosphor, the type and content of the heatdispersing particles and the addition and the type of the couplingagent. In addition, the particle size and the particle size distributionof the heat dispersing particles would also affect the thermalconductivity.

The organosilicon-modified polyimide resin composition may also comprisephosphor for obtaining the desired light-emitting properties. Thephosphor can convert the wavelength of the light emitted from thelight-emitting semiconductor. For example, yellow phosphor can convertblue light to yellow light, and red phosphor can convert blue light tored light. Examples of yellow phosphor include transparent phosphor suchas (Ba,Sr,Ca)₂SiO₄:Eu, and (Sr,Ba)₂SiO₄:Eu(barium orthosilicate (BOS));silicate-type phosphor having a silicate structure such asY₃Al₅O₁₂:Ce(YAG(yttrium.aluminum.garnet): Ce), andTb₃Al₃O₁₂:Ce(YAG(terbium.aluminum.garnet):Ce); and oxynitride phosphorsuch as Ca-α-SiAlON. Examples of red phosphor include nitride phosphor,such as CaAlSiN₃:Eu, and CaSiN₂:Eu. Examples of green phosphor includerare earth-halide phosphor, and silicate phosphor. The ratio of thephosphor in the organosilicon-modified polyimide resin composition maybe determined arbitrarily according to the desired light-emittingproperty. In addition, since the phosphor have a thermal conductivitywhich is significantly higher than that of the organosilicon-modifiedpolyimide resin, the thermal conductivity of the organosilicon-modifiedpolyimide resin composition as a whole will increase as the ratio of thephosphor in the organosilicon-modified polyimide resin compositionincreases. Accordingly, in an embodiment, as long as the light-emittingproperty is fulfilled, the content of the phosphor can be suitablyincreased to increase the thermal conductivity of theorganosilicon-modified polyimide resin composition, which is beneficialto the heat dissipation of the filament substrate or thelight-conversion layer. Furthermore, when the organosilicon-modifiedpolyimide resin composition is used as the filament substrate, thecontent, shape and particle size of the phosphor in theorganosilicon-modified polyimide resin composition also have certaineffect on the mechanical property (such as the elastic modulus,elongation, tensile strength) and the warpage extent of the substrate.In order to render superior mechanical property and thermal conductivityas well as small warpage extent to the substrate, the phosphor includedin the organosilicon-modified polyimide resin composition areparticulate, and the shape thereof may be sphere, plate or needle,preferably sphere. The maximum average length of the phosphor (theaverage particle size when they are spherical) is above 0.1 μm,preferably over 1 μm, further preferably 1˜100 μm, and more preferably1˜50 μm. The content of phosphor is no less than 0.05 times, preferablyno less than 0.1 times, and no more than 8 times, preferably no morethan 7 times, the weight of the organosilicon-modified polyimide. Forexample, when the weight of the organosilicon-modified polyimide is 100parts in weight, the content of the phosphor is no less than 5 parts inweight, preferably no less than 10 parts in weight, and no more than 800parts in weight, preferably no more than 700 parts in weight. When thecontent of the phosphor in the organosilicon-modified polyimide resincomposition exceeds 800 parts in weight, the mechanical property of theorganosilicon-modified polyimide resin composition may not achieve thestrength as required for a filament substrate, resulting in the increaseof the defective rate of the product. In an embodiment, two kinds ofphosphor are added at the same time. For example, when red phosphor andgreen phosphor are added at the same time, the added ratio of redphosphor to green phosphor is 1:5˜8, preferably 1:6˜7. In anotherembodiment, red phosphor and yellow phosphor are added at the same time,wherein the added ratio of red phosphor to yellow phosphor is 1:5˜8,preferably 1:6˜7. In another embodiment, three or more kinds of phosphorare added at the same time.

The main purposes of adding the heat dispersing particles are toincrease the thermal conductivity of the organosilicon-modifiedpolyimide resin composition, to maintain the color temperature of thelight emission of the LED chip, and to prolong the service life of theLED chip. Examples of the heat dispersing particles include silica,alumina, magnesia, magnesium carbonate, aluminum nitride, boron nitrideand diamond. Considering the dispersity, silica, alumina or combinationthereof is preferably. The shape of the heat dispersing particles may besphere, block, etc., where the sphere shape encompasses shapes which aresimilar to sphere. In an embodiment, heat dispersing particles may be ina shape of sphere or non-sphere, to ensure the dispersity of the heatdispersing particles and the thermal conductivity of the substrate,wherein the added weight ratio of the spherical and non-spherical heatdispersing particles is 1:0.15˜0.35.

Table 3-1 shows the relationship between the content of the heatdispersing particles and the thermal conductivity of theorganosilicon-modified polyimide resin composition. As the content ofthe heat dispersing particles increases, the thermal conductivity of theorganosilicon-modified polyimide resin composition increases. However,when the content of the heat dispersing particles in theorganosilicon-modified polyimide resin composition exceeds 1200 parts inweight, the mechanical property of the organosilicon-modified polyimideresin composition may not achieve the strength as required for afilament substrate, resulting in the increase of the defective rate ofthe product. In an embodiment, high content of heat dispersing particleswith high light transmittance or high reflectivity (such as SiO₂, Al₂O₃)may be added, which, in addition to maintaining the transmittance of theorganosilicon-modified polyimide resin composition, increases the heatdissipation of the organosilicon-modified polyimide resin composition.The heat conductivities shown in Tables 3-1 and 3-2 were measured by athermal conductivity meter DRL-III manufactured by Xiangtan cityinstruments Co., Ltd. under the following test conditions: heatingtemperature: 90° C.; cooling temperature: 20° C.; load: 350N, aftercutting the resultant organosilicon-modified polyimide resin compositioninto test pieces having a film thickness of 300 μm and a diameter of 30mm.

TABLE 3-1 Weight Ratio [wt %] 0.0% 37.9% 59.8% 69.8% 77.6% 83.9% 89.0%Volume Ratio [vol %] 0.0% 15.0% 30.0% 40.0% 50.0% 60.0% 70.0% ThermalConductivity [W/m * K] 0.17 0.20 0.38 0.54 0.61 0.74 0.81

TABLE 3-2 Specification 1 2 3 4 5 6 7 Average Particle Size [μm] 2.7 6.6  9.0  9.6  13 4.1  12 Particle Size Distribution [μm] 1~7 1~20 1~300.2~30 0.2~110 0.1~20 0.1~100 Thermal Conductivity [W/m * K] 1.65 1.481.52 1.86 1.68 1.87 2.10

For the effects of the particle size and the particle size distributionof the heat dispersing particles on the thermal conductivity of theorganosilicon-modified polyimide resin composition, see both Table 3-2and FIG. 2. Table 3-2 and FIG. 2 show seven heat dispersing particleswith different specifications added into the organosilicon-modifiedpolyimide resin composition in the same ratio and their effects on thethermal conductivity. The particle size of the heat dispersing particlessuitable to be added to the organosilicon-modified polyimide resincomposition can be roughly classified as small particle size (less than1 μm), medium particle size (1˜30 μm) and large particle size (above 30μm).

Comparing specifications 1, 2 and 3, wherein only heat dispersingparticles with medium particle size but different average particle sizesare added, when only heat dispersing particles with medium particle sizeare added, the average particle size of the heat dispersing particlesdoes not significantly affect the thermal conductivity of theorganosilicon-modified polyimide resin composition. Comparingspecifications 3 and 4, wherein the average particle sizes are similar,the specification 4 comprising small particle size and medium particlesize obviously exhibits higher thermal conductivity than specification 3comprising only medium particle size. Comparing specifications 4 and 6,which comprise heat dispersing particles with both small particle sizeand medium particle size, although the average particle sizes of theheat dispersing particles are different, they have no significant effecton the thermal conductivity of the organosilicon-modified polyimideresin composition. Comparing specifications 4 and 7, specification 7,which comprises heat dispersing particles with large particle size inaddition to small particle size and medium particle size, exhibits themost excellent thermal conductivity. Comparing specifications 5 and 7,which both comprise heat dispersing particles with large, medium andsmall particle sizes and have similar average particle sizes, thethermal conductivity of specification 7 is significantly superior tothat of specification 5 due to the difference in the particle sizedistribution. See FIG. 2 for the particle size distribution ofspecification 7, the curve is smooth, and the difference in the slope issmall, showing that specification 7 not only comprises each particlesize, but also have moderate proportions of each particle size, and theparticle size is normally distributed. For example, the small particlesize represents about 10%, the medium particle size represents about60%, and the large particle size represents about 30%. In contrast, thecurve for specification 5 has two regions with large slopes, whichlocate in the region of particle size 1˜2 μm and particle size 30˜70 μm,respectively, indicating that most of the particle size in specification5 is distributed in particle size 1˜2 μm and particle size 30˜70 μm, andonly small amount of heat dispersing particles with particle size 3˜20μm are present, i.e. exhibiting a two-sided distribution.

Accordingly, the extent of the particle size distribution of the heatdispersing particles affecting the thermal conductivity is greater thanthat of the average particle size of the heat dispersing particles. Whenlarge, medium and small particle sizes of the heat dispersing particlesare added, and the small particle size represents about 5˜20%, themedium particle size represents about 50˜70%, and large particle sizerepresents about 20˜40%, the organosilicon-modified polyimide resin willhave optimum thermal conductivity. That is because when large, mediumand small particle sizes are present, there would be denser packing andcontacting each other of heat dispersing particles in a same volume, soas to form an effective heat dissipating route.

In an embodiment, for example, alumina with a particle size distributionof 0.1˜100 μm and an average particle size of 12 μm or with a particlesize distribution of 0.1˜20 μm and an average particle size of 4.1 μm isused, wherein the particle size distribution is the range of theparticle size of alumina. In another embodiment, considering thesmoothness of the substrate, the average particle size may be selectedas ⅕˜⅖, preferably ⅕˜⅓ of the thickness of the substrate. The amount ofthe heat dispersing particles may be 1˜12 times the weight (amount) ofthe organosilicon-modified polyimide. For example, if the amount of theorganosilicon-modified polyimide is 100 parts in weight, the amount ofthe heat dispersing particles may be 100˜1200 parts in weight,preferably 400˜900 parts in weight. Two different heat dispersingparticles such as silica and alumina may be added at the same time,wherein the weight ratio of alumina to silica may be 0.4˜25:1,preferably 1˜10:1.

In the synthesis of the organosilicon-modified polyimide resincomposition, a coupling agent such as a silicone coupling agent may beadded to improve the adhesion between the solid material (such as thephosphor and/or the heat dispersing particles) and the adhesive material(such as the organosilicon-modified polyimide), and to improve thedispersion uniformity of the whole solid materials, and to furtherimprove the heat dissipation and the mechanical strength of thelight-conversion layer. The coupling agent may also be titanate couplingagent, preferably epoxy titanate coupling agent. The amount of thecoupling agent is related to the amount of the heat dispersing particlesand the specific surface area thereof. The amount of the couplingagent=(the amount of the heat dispersing particles*the specific surfacearea of the heat dispersing particles)/the minimum coating area of thecoupling agent. For example, when an epoxy titanate coupling agent isused, the amount of the coupling agent=(the amount of the heatdispersing particles*the specific surface area of the heat dispersingparticles)/331.5.

In other specific embodiments of the present invention, in order tofurther improve the properties of the organosilicon-modified polyimideresin composition in the synthesis process, an additive such as adefoaming agent, a leveling agent or an adhesive may be selectivelyadded in the process of synthesizing the organosilicon-modifiedpolyimide resin composition, as long as it does not affect lightresistance, mechanical strength, heat resistance and chromism of theproduct. The defoaming agent is used to eliminate the foams produced inprinting, coating and curing. For example, acrylic acid or siliconesurfactants may be used as the defoaming agent. The leveling agent isused to eliminate the bumps in the film surface produced in printing andcoating. Specifically, adding preferably 0.01˜2 wt % of a surfactantcomponent can inhibit foams. The coating film can be smoothened by usingacrylic acid or silicone leveling agents, preferably non-ionicsurfactants free of ionic impurities. Examples of the adhesive includeimidazole compounds, thiazole compounds, triazole compounds,organoaluminum compounds, organotitanium compounds and silane couplingagents. Preferably, the amount of these additives is no more than 10% ofthe weight of the organosilicon-modified polyimide. When the mixedamount of the additive exceeds 10 wt %, the physical properties of theresultant coating film tend to decline, and it even leads todeterioration of the light resistance due to the presence of thevolatile components.

Mechanical Strength

The factors affecting the mechanical strength of theorganosilicon-modified polyimide resin composition include at least thetype of the main material, the siloxane content, the type of themodifier (thermal curing agent), the phosphor and the content of theheat dispersing particles.

Different organosilicon-modified polyimide resins have differentproperties. Table 4 lists the main properties of the fluorinatedaromatic, semi-aliphatic and full aliphatic organosilicon-modifiedpolyimide, respectively, with a siloxane content of about 45% (wt %).The fluorinated aromatic has the best resistance to thermo chromism. Thefull aliphatic has the best light transmittance. The fluorinatedaromatic has both high tensile strength and high elastic modulus. Theconditions for testing the mechanical strengths shown in Table 4-6: theorganosilicon-modified polyimide resin composition has a thickness of 50μm and a width of 10 mm, and the tensile strength of the film isdetermined according to ISO527-3:1995 standard with a drawing speed of10 mm/min.

TABLE 4 Elongation Organosilicon- Siloxane Thermal Tensile Elastic atResistance Modified Content Curing Strength Modulus Break to Polyimide(wt %) Agent (MPa) (GPa) (%) Transmittance Thermochromism Fluorinated 44X22-163 22.4 1.0 83 96 95 Aromatic Semi-Aliphatic 44 X22-163 20.4 0.9 3096 91 Full Aliphatic 47 X22-163 19.8 0.8 14 98 88

TABLE 5 Addition Elongation Siloxane of Thermal Tensile Elastic atResistance Content Phosphor, Curing Tg Strength Modulus Break Chemicalto (wt %) Alumina Agent (° C.) (MPa) (GPa) (%) Transmittance ResistanceThermochromism 37 x BPA 158 33.2 1.7 10 85 Δ 83 37 ∘ BPA — 26.3 5.1 0.7— — — 41 x BPA 142 38.0 1.4 12 92 ∘ 90 41 ∘ BPA — 19.8 4.8 0.8 — — — 45x BPA 145 24.2 1.1 15 97 Δ 90 45 ∘ BPA — 21.5 4.2 0.9 — — — 64 x BPA  308.9 0.04 232 94 ∘ 92 64 ∘ BPA — 12.3 3.1 1.6 — — — 73 x BPA  0 1.8 0.001291 96 ∘ 95 73 ∘ BPA — 9.6 2.5 2 — — —

TABLE 6 Thermal Curing Transmittance (%) Mechanical StrengthOrganosilicon- Agent Film Tensile Modified Amount Thickness ElongationStrength Polyimides Types (%) 380 nm 410 nm 450 nm (μm) (%) (MPa) FullAliphatic BPA 8.0 87.1 89.1 90.6 44 24.4 10.5 Full Aliphatic X22-163 8.086.6 88.6 90.2 40 43.4 8.0 Full Aliphatic KF105 12.0 87.5 89.2 90.8 4380.8 7.5 Full Aliphatic EHPE3150 7.5 87.1 88.9 90.5 44 40.9 13.1 FullAliphatic 2021p 5.5 86.1 88.1 90.1 44 64.0 12.5

In the manufacture of the filament, the LED chip and the electrodes arefirst fixed on the filament substrate formed by theorganosilicon-modified polyimide resin composition with a die bondingglue, followed by a wiring procedure, in which electric connections areestablished between adjacent LED chips and between the LED chip and theelectrode with wires. To ensure the quality of die bonding and wiring,and to improve the product quality, the filament substrate should have acertain level of elastic modulus to resist the pressing force in the diebonding and wiring processes. Accordingly, the filament substrate shouldhave an elastic modulus more than 2.0 GPa, preferably 2˜6 GPa, morepreferably 4˜6 GPa. Table 5 shows the effects of different siloxanecontents and the presence of particles (phosphor and alumina) on theelastic modulus of the organosilicon-modified polyimide resincomposition. Where no fluorescent powder or alumina particle is added,the elastic modulus of the organosilicon-modified polyimide resincomposition is always less than 2.0 GPa, and as the siloxane contentincreases, the elastic modulus tends to decline, i.e. theorganosilicon-modified polyimide resin composition tends to soften.However, where phosphor and alumina particles are added, the elasticmodulus of the organosilicon-modified polyimide resin composition may besignificantly increased, and is always higher than 2.0 GPa. Accordingly,the increase in the siloxane content may lead to softening of theorganosilicon-modified polyimide resin composition, which isadvantageous for adding more fillers, such as more phosphor or heatdispersing particles. In order for the substrate to have superiorelastic modulus and thermal conductivity, appropriate particle sizedistribution and mixing ratio may be selected so that the averageparticle size is within the range from 0.1 μm to 100 μm or from 1 μm to50 μm.

In order for the LED filament to have good bending properties, thefilament substrate should have an elongation at break of more than 0.5%,preferably 1˜5%, most preferably 1.5˜5%. As shown in Table 5, where nofluorescent powder or alumina particle is added, theorganosilicon-modified polyimide resin composition has excellentelongation at break, and as the siloxane content increases, theelongation at break increases and the elastic modulus decreases, therebyreducing the occurrence of warpage. In contrast, where phosphor andalumina particles are added, the organosilicon-modified polyimide resincomposition exhibits decreased elongation at break and increased elasticmodulus, thereby increasing the occurrence of warpage.

By adding a thermal curing agent, not only the heat resistance and theglass transition temperature of the organosilicon-modified polyimideresin are increased, the mechanical properties, such as tensilestrength, elastic modulus and elongation at break, of theorganosilicon-modified polyimide are also increased. Adding differentthermal curing agents may lead to different levels of improvement. Table6 shows the tensile strength and the elongation at break of theorganosilicon-modified polyimide resin composition after the addition ofdifferent thermal curing agents. For the full aliphaticorganosilicon-modified polyimide, the addition of the thermal curingagent EHPE3150 leads to good tensile strength, while the addition of thethermal curing agent KF105 leads to good elongation.

TABLE 7 Specific Information of BPA Content of Equivalent ProductViscosity at Color Hydrolysable Epoxy Hue Name 25° C.(mPa.s) (G)Chlorine (mg/kg) (g/mol) APHA BPA 11000~15000 ≤1 ≤300 184~194 ≤30

TABLE 8 Specific Information of 2021P Specific Melting Boiling WaterProduct Viscosity Gravity Point Point Content Equivalent of Hue Name at25° C. (mPa · s) (25/25° C.) (° C.) (° C./4 hPa) (%) Epoxy (g/mol) APHA2021P 250 1.17 −20 188 0.01 130 10

TABLE 9 Specific Information of EHPE3150 and EHPE3150CE ViscosityEquivalent at of Product 25° C. Softening Epoxy(g/ Hue Name (mPa.s)Appearance Point mol) APHA EHPE3150 — Transparent 75 177 20 (in PlateSolid 25% acetone solution) EHPE3150CE 50,000 Light — 151 60 YellowTransparent Liquid

TABLE 10 Specific Information of PAME, KF8010, X22-161A, X22-161B,NH15D, X22-163, X22-163A and KF-105 Equivalent Specific Refractive ofProduct Viscosity at Gravity Index at Functional Name 25° C.(mm2/s) at25° C. 25° C. Group PAME 4 0.90 1.448 130 g/mol KF8010 12 1.00 1.418 430g/mol X22-161A 25 0.97 1.411 800 g/mol X22-161B 55 0.97 1.408 1500 g/molNH15D 13 0.95 1.403 1.6~2.1 g/mmol X22-163 15 1.00 1.450 200 g/molX22-163A 30 0.98 1.413 1000 g/mol KF-105 15 0.99 1.422 490 g/mol

The organosilicon-modified polyimide resin composition of the presentembodiment may be used in a form of film or as a substrate together witha support to which it adheres. The film forming process comprises threesteps: (a) coating step: spreading the above organosilicon-modifiedpolyimide resin composition on a peelable body by coating to form afilm; (b) heating and drying step: heating and drying the film togetherwith the peelable body to remove the solvent from the film; and (c)peeling step: peeling the film from the peelable body after the dryingis completed to give the organosilicon-modified polyimide resincomposition in a form of film. The above peelable body may be acentrifugal film or other materials which do not undergo chemicalreaction with the organosilicon-modified polyimide resin composition,e.g., PET centrifugal film.

The organosilicon-modified polyimide resin composition may be adhered toa support to give an assembly film, which may be used as the substrate.The process of forming the assembly film comprises two steps: (a)coating step: spreading the above organosilicon-modified polyimide resincomposition on a support by coating to from an assembly film; and (b)heating and drying step: heating and drying the assembly film to removethe solvent from the film.

In the coating step, roll-to-roll coating devices such as roller coater,mold coating machine and blade coating machine, or simple coating meanssuch as printing, inkjeting, dispensing and spraying may be used.

The drying method in the above heating and drying step may be drying invacuum, drying by heating, or the like. The heating may be achieved by aheat source such as an electric heater or a heating media to produceheat energy and indirect convection, or by infrared heat radiationemitted from a heat source.

A film (composite film) with high thermal conductivity can be obtainedfrom the above organosilicon-modified polyimide resin composition bycoating and then drying and curing, so as to achieve any one orcombination of the following properties: superior light transmittance,chemical resistance, heat resistance, thermal conductivity, filmmechanical property and light resistance. The temperature and time inthe drying and curing step may be suitably selected according to thesolvent and the coated film thickness of the organosilicon-modifiedpolyimide resin composition. The weight change of theorganosilicon-modified polyimide resin composition before and after thedrying and curing as well as the change in the peaks in the IR spectrumrepresenting the functional groups in the thermal curing agent can beused to determine whether the drying and curing are completed. Forexample, when an epoxy resin is used as the thermal curing agent,whether the difference in the weight of the organosilicon-modifiedpolyimide resin composition before and after the drying and curing isequal to the weight of the added solvent as well as the increase ordecrease of the epoxy peak before and after the drying and curing areused to determine whether the drying and curing are completed.

In an embodiment, the amidation is carried out in a nitrogen atmosphere,or vacuum defoaming is employed in the synthesis of theorganosilicon-modified polyimide resin composition, or both, so that thevolume percentage of the cells in the organosilicon-modified polyimideresin composition composite film is 5˜20%, preferably 5˜10%. As shown inFIG. 3B, the organosilicon-modified polyimide resin compositioncomposite film is used as the substrate for the LED soft filament. Thesubstrate 420 b has an upper surface 420 b 1 and an opposite lowersurface 420 b 2. FIG. 3A shows the surface morphology of the substrateafter gold is scattered on the surface thereof as observed with vega3electron microscope from Tescan Corporation. As can be seen from FIG. 3Band the SEM image of the substrate surface shown in FIG. 3A, there is acell 4 d in the substrate, wherein the cell 4 d represents 5˜20% byvolume, preferably 5˜10% by volume, of the substrate 420 b, and thecross section of the cell 4 d is irregular. FIG. 3B shows thecross-sectional scheme of the substrate 420 b, wherein the dotted lineis the baseline. The upper surface 420 b 1 of the substrate comprises afirst area 4 a and a second area 4 b, wherein the second area 4 bcomprises a cell 4 d, and the first area 4 a has a surface roughnesswhich is less than that of the second area 4 b. The light emitted by theLED chip passes through the cell in the second area and is scattered, sothat the light emission is more uniform. The lower surface 420 b 2 ofthe substrate comprises a third area 4 c, which has a surface roughnesswhich is higher than that of the first area 4 a. When the LED chip ispositioned in the first area 4 a, the smoothness of the first area 4 ais favorable for subsequent bonding and wiring. When the LED chip ispositioned in the second area 4 b or the third area 4 c, the area ofcontact between the die bonding glue and substrate is large, whichimproves the bonding strength between the die bonding glue andsubstrate. Therefore, by positioning the LED chip on the upper surface420 b 1, bonding and wiring as well as the bonding strength between thedie bonding glue and substrate can be ensured at the same time. When theorganosilicon-modified polyimide resin composition is used as thesubstrate of the LED soft filament, the light emitted by the LED chip isscattered by the cell in the substrate, so that the light emission ismore uniform, and glare can be further improved at the same time. In anembodiment, the surface of the substrate 420 b may be treated with asilicone resin or a titanate coupling agent, preferably a silicone resincomprising methanol or a titanate coupling agent comprising methanol, ora silicone resin comprising isopropanol. The cross section of thetreated substrate is shown in FIG. 3C. The upper surface 420 b 1 of thesubstrate has relatively uniform surface roughness. The lower surface420 b 2 of the substrate comprises a third area 4 c and a fourth area 4e, wherein the third area 4 c has a surface roughness which is higherthan that of the fourth area 4 e. The surface roughness of the uppersurface 420 b 1 of the substrate may be equal to that of the fourth area4 e. The surface of the substrate 420 b may be treated so that amaterial with a high reactivity and a high strength can partially enterthe cell 4 d, so as to improve the strength of the substrate.

When the organosilicon-modified polyimide resin composition is preparedby vacuum defoaming, the vacuum used in the vacuum defoaming may be−0.5˜−0.09 MPa, preferably −0.2˜−0.09 MPa. When the total weight of theraw materials used in the preparation of the organosilicon-modifiedpolyimide resin composition is less than or equal to 250 g, therevolution speed is 1200˜2000 rpm, the rotation speed is 1200˜2000 rpm,and time for vacuum defoaming is 3˜8 min. This not only maintainscertain amount of cells in the film to improve the uniformity of lightemission, but also keeps good mechanical properties. The vacuum may besuitably adjusted according to the total weight of the raw materialsused in the preparation of the organosilicon-modified polyimide resincomposition. Normally, when the total weight is higher, the vacuum maybe reduced, while the stirring time and the stirring speed may besuitably increased.

According to the present disclosure, a resin having superiortransmittance, chemical resistance, resistance to thermochromism,thermal conductivity, film mechanical property and light resistance asrequired for a LED soft filament substrate can be obtained. In addition,a resin film having a high thermal conductivity can be formed by simplecoating methods such as printing, inkjeting, and dispensing.

When the organosilicon-modified polyimide resin composition compositefilm is used as the filament substrate (or base layer), the LED chip isa hexahedral luminous body. In the production of the LED filament, atleast two sides of the LED chip are coated by a top layer. When theprior art LED filament is lit up, non-uniform color temperatures in thetop layer and the base layer would occur, or the base layer would give agranular sense. Accordingly, as a filament substrate, the composite filmis required to have superior transparency. In other embodiments,sulfonyl group, non-coplanar structure, meta-substituted diamine, or thelike may be introduced into the backbone of the organosilicon-modifiedpolyimide to improve the transparency of the organosilicon-modifiedpolyimide resin composition. In addition, in order for the bulbemploying said filament to achieve omnidirectional illumination, thecomposite film as the substrate should have certain flexibility.Therefore, flexible structures such as ether (such as(4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether), carbonyl,methylene may be introduced into the backbone of theorganosilicon-modified polyimide. In other embodiments, a diamine ordianhydride comprising a pyridine ring may be employed, in which therigid structure of the pyridine ring can improve the mechanicalproperties of the composite film. Meanwhile, by using it together with astrong polar group such as —F, the composite film may have superiorlight transmittance. Examples of the anhydride comprising a pyridinering include2,6-bis(3′,4′-dicarboxyphenyl)-4-(3″,5″-bistrifluoromethylphenyl)pyridinedianhydride.

The LED filament structure in the aforementioned embodiments is mainlyapplicable to the LED light bulb product, so that the LED light bulb canachieve the omni-directional light illuminating effect through theflexible bending characteristics of the single LED filament. Thespecific embodiment in which the aforementioned LED filament applied tothe LED light bulb is further explained below.

Please refer to FIG. 4A. FIG. 4A illustrates a perspective view of anLED light bulb according to an embodiment of the present disclosure.According to the embodiment, the LED light bulb 20 c comprises a lamphousing 12, a bulb base 16 connected with the lamp housing 12, twoconductive supports 51 a, 51 b disposed in the lamp housing 12, adriving circuit 518 electrically connected with both the conductivesupports 51 a, 51 b and the bulb base 16, a stem 19, supporting arms 15and a single LED filament 100.

The lamp housing 12 is a material which is preferably light transmissiveor thermally conductive, such as, glass or plastic, but not limitedthereto. In implementation, the lamp housing 12 may be doped with agolden yellow material or its surface coated with a yellow film toabsorb a portion of the blue light emitted by the LED chip to reduce thecolor temperature of the light emitted by the LED light bulb 20 c. Inother embodiments of the present invention, the lamp housing 12 includesa layer of luminescent material (not shown), which may be formed on theinner surface or the outer surface of the lamp housing 12 according todesign requirements or process feasibility, or even integrated in thematerial of the lamp housing 12. The luminescent material layercomprises low reabsorption semiconductor nanocrystals (hereinafterreferred to as quantum dots), the quantum dots comprises a core, aprotective shell and a light absorbing shell, and the light absorbingshell is disposed between the core and the protective shell. The coreemits the emissive light with emission wavelength, and the lightabsorbing shell emits the excited light with excitation wavelength. Theemission wavelength is longer than the excitation wavelength, and theprotective shell provides the stability of the light.

The LED filament 100 shown in FIG. 4A is bent to form a contourresembling to a circle while being observed from the top view of FIG.4A. The shape of the LED filament 100 is novel and makes theillumination more uniform. In comparison with a LED bulb having multipleLED filaments, single LED filament 100 has less connecting spots. Inimplementation, single LED filament 100 has only two connecting spotssuch that the probability of defect soldering or defect mechanicalpressing is decreased.

The stem 19 has a stand 19 a extending to the center of the lamp housing12. The stand 19 a supports the supporting arms 15. The first end ofeach of the supporting arms 15 is connected with the stand 19 a whilethe second end of each of the supporting arms 15 is connected with theLED filament 100.

The supporting arms 15 may be, but not limited to, made of carbon steelspring to provide with adequate rigidity and flexibility so that theshock to the LED light bulb caused by external vibrations is absorbedand the LED filament 100 is not easily to be deformed. Since the stand19 a extending to the center of the lamp housing 12 and the supportingarms 15 are connected to a portion of the stand 19 a near the topthereof, the position of the LED filaments 100 is at the level close tothe center of the lamp housing 12. Accordingly, the illuminationcharacteristics of the LED light bulb 20 c are close to that of thetraditional light bulb including illumination brightness. Theillumination uniformity of LED light bulb 20 c is better. In theembodiment, at least a half of the LED filament 100 is around a centeraxle of the LED light bulb 20 c. The center axle is coaxial with theaxle of the stand 19 a.

In the embodiment, the first end of the supporting arm 15 is connectedwith the stand 19 a of the stem 19. In an embodiment where the stem 19is made of glass, the stem 19 would not be cracked or exploded becauseof the thermal expansion of the supporting arms 15 of the LED light bulb20 c. Additionally, there may be no stand in an LED light bulb. Thesupporting arm 15 may be fixed to the stem or the lamp housing directlyto eliminate the negative effect to illumination caused by the stand.

The supporting arm 15 is thus non-conductive to avoid a risk that theglass stem 19 may crack due to the thermal expansion and contraction ofthe metal filament in the supporting arm 15 under the circumstances thatthe supporting arm 15 is conductive and generates heat when currentpasses through the supporting arm 15.

In different embodiments, the second end of the supporting arm 15 may bedirectly inserted inside the LED filament 100 and become an auxiliarypiece in the LED filament 100, which can enhance the mechanical strengthof the LED filament 100.

The LED filament 100 shown in FIG. 4A is curved to form a circular shapein a top view while the LED filament is curved to form a wave shape in aside view. The wave shaped structure is not only novel in appearance butalso guarantees that the LED filament 100 illuminates evenly. In themeantime, the single LED filament 100, comparing to multiple LEDfilaments, requires less joint points (e.g., pressing points, fusingpoints, or welding points) for being connected to the conductivesupports 51 a, 51 b. In practice, the single LED filament 100 (as shownin FIG. 4A) requires only two joint points respectively formed on thetwo conductive electrodes, which effectively lowers the risk of faultwelding and simplifies the process of connection compared to themechanically connection in the tightly pressing manner.

Please refer to FIG. 4B. FIG. 4B is a projection of a top view of an LEDfilament of the LED light bulb 20 c of FIG. 4A. As shown in FIG. 4B, inan embodiment, the LED filament may be curved to form a wave shaperesembling a circle observed in a top view to surround the center of thelight bulb or the stem. In different embodiments, the LED filamentobserved in the top view can form a quasi-circle or a quasi U shape.

In an embodiment, the LED light bulb 20 c shown in FIG. 4A may be alight bulb with an A size. The two joint points for electricalconnection between the two conductive supports 51 a, 51 b and the LEDfilament 100 is spaced by a distance, which is within 3 cm and ispreferably within 2 cm. The LED filament 100 surrounds with the waveshape; therefore, the LED filament 100 may generate an effect of anomnidirectional light, and the two joint points may be close to eachother such that the conductive supports 51 a, 51 b are substantiallybelow the LED filament 100. Visually, the conductive supports 51 a, 51 bkeeps a low profile and is integrated with the LED filament 100 to showan elegance curvature. While being observed from a side of the LEDfilament 100 in the LED light bulb 20 c, a distance between the highestpoint and the lowest point of the wave of the LED filament 100 is from2.2 cm to 3.8 cm and is preferably from 2.2 cm to 2.8 cm. Thus it couldbe ensured that there would be a space for heat dissipation above theLED filament 100.

As shown in FIG. 4A, the shape of the LED filament 100 may satisfy acurve equation. The position of the LED filament 100 in space relates tothe Cartesian coordinates (i.e., an xyz coordinates) shown in FIG. 4A.An x-y plane of the xyz coordinates is a plane passing through a top ofthe stem 19 (i.e., a top of the stand 19 a in the embodiment in whichthe stand 19 a is deemed as a part of the stem 19). An origin of the xyzcoordinates is at the top of the stem 19 (the origin may be at a centerof a sphere body of a lamp housing of a light bulb without any stems).The x-y plane is perpendicular to a height direction of the LED lightbulb 20 c.

The two conductive electrodes (i.e., the welding points, the jointpoints, the contacting points, or the fusing points) are symmetricallydisposed at two sides of a y-axis of the xyz coordinates. A z-axis ofthe xyz coordinates is coaxial with stem 19 (or is coaxial with acentral axis passing through a horizontal plane of the LED light bulb 20c). The shape of the LED filament 100 varies along an x-direction, ay-direction, and a z-direction according to t, and t is a variablebetween 0 and 1. A position of points of the LED filament 100 in the xyzcoordinates is defined as X, Y, and Z and satisfies the curve equation.Herein, the term “points of the LED filament” means “most of points ofthe LED filament”, or “more than 60% of points of the LED filament.” Thecurve equation is:X=m1*cos(t*360),Y=m2*sin(t*360),Z=n*cos(t*360*k),

The LED filament 100 varies along the x-direction, the y-direction, andthe z-direction according to t. When X=0, |Y|max=m2 (a max value of |Y|is m2), and |Z|max=n (a max value of |Z| is n). When Y=0, |X|max=m1 (amax value of |X| is m1), and |Z|max=n (the max value of |Z| is n). WhenZ=0, |X|max=m1 (the max value of |X| is m1), and |Y|max=m2 (the maxvalue of |Y| is m2). m1 is a length (projection length) in thex-direction, and 24≤m1≤27 (mm). m2 is a length (projection length) inthe y-direction, and 24≤m2≤27 (mm). Based upon the above configuration,the LED filament 100 in the lamp housing 12 may provide good luminousflux. n is a height of the highest point of the LED filament 100 fromthe x-y plane in the z-direction, and 0<n≤14 (mm). Based upon the abovecondition, wires in turning points of the LED filament 100 may hard tobreak. k is a number of the highest point(s). The more the supportingarms (or supporting bars), the hard the manufacture is; therefore, k isconfigured as: 2≤k≤8. A curve line drawn by the above curve equation maybe deemed as a reference for the LED filament 100 being distributed inspace. According to conditions of different arts and equipment, theconfiguration of the LED filament 100 in practice may have about 0 to25% in spatial difference different from the reference based upon thecurve equation. Certain region(s) on the filament with supportingpoint(s) may be relatively highest point(s) and lowest point(s). Thespatial difference of the certain region(s) may be less, e.g., 0 to 20%.In an embodiment, r is the radius of a cross section of the lamp housingon the horizontal plane. Cross sections of the lamp housing on thehorizontal plane from the bottom to the top of the lamp housing alongthe height direction may have varied radii, and the radius r is the onewith the largest value. In such case, the values of m1, m2, and n may beset as: 0.8*r≤m1≤10.9*r; 0.8*r≤m2≤0.9*r; 0<n≤0.47*r. Additionally, p isthe radius of an interface of the bulb base utilized for being connectedto the lamp housing, G is the length of the LED filament, and, in suchcase, the values of G may be set as: 1.2*p≤G≤5.6*r. Based upon the abovesetting, the LED filament may not only achieve the aforementionedeffect, but may also need the least length and the least number of theLED chips. As a result, the cost of materials for the manufacture of theLED light bulb may reduce, and the temperature of the LED light bulbduring operation can be suppressed.

Referring to FIGS. 5A to 5D, FIG. 5A is a perspective diagram of an LEDlight bulb 40 h according to an embodiment of the present invention, andFIGS. 5B to 5D are respectively side view, another side view, and topview of the FIG. 5A. In the present embodiment, the LED light bulb 40 hincludes a lamp housing 12, a bulb base 16 connected to the lamp housing12, a stem 19, a stand 19 a, and a single LED filament 100. The LEDfilament 100 includes two conductive electrodes 110, 112 at two ends, aplurality of LED sections 102, 104 and a single conductive section 130.Moreover, the LED light bulb 40 h and the single LED filament 100disposed in the LED light bulb 40 h can refer to related descriptions ofthe previous embodiments.

Referring to FIGS. 5A to 5D, in the present invention, the LED filament100 includes one conductive section 130, two LED sections 102, 104, andbetween two adjacent LED sections 102, 104 is connected by theconductive section 130. Wherein the LED filament 100 having a circulararc at the highest point of the bending curvature, that is, each of theLED sections 102, 104 respectively having a circular arc at the highestpoint of the LED filament 100 in the Z direction, and the conductivesection also exhibits a circular arc at the low point of the LEDfilament in the Z direction. Moreover, the LED filament 100 can bedefined as having a plurality of sections, each of the sections isconnected between the first and second conductive sections 130, and eachLED section 102, 104 is formed into a respective section.

Moreover, since the LED filament 100 is equipped with a flexible baselayer, the flexible base layer preferably is made by anorganosilicon-modified polyimide resin composition, and thus the LEDsections 102, 104 themselves also have a certain degree of bendability.In the present embodiment, the two LED sections 102, 104 arerespectively bent to form in the shape like an inverted deformed Uletter, and the conductive section 130 is located between the two LEDsections 102, 104, and the degree of the bending of the conductivesection 130 is the same as or greater than the degree of the bending ofthe LED sections 102, 104. In other words, the two LED sections 102, 104of the LED filament are respectively bent at the high point to form inthe shape like an inverted deformed U letter and have a bending radiusvalue at R1, and the conductive section 130 is bent at a low point ofthe LED filament 100 and has a bending radius value at R2, wherein thevalue R1 is the same as or greater than the value R2. Through theconfiguration of the conductive section 130, the LED filament 100disposing in a limited space can be realized with a small radius bendingof the LED filament 100. In one embodiment, the bending points of theLED sections 102, 104 are at the same height in the Z direction.Further, in the Z direction, the stand 19 a of the present embodimenthas a lower position than the stand 19 a of the previous embodiment, andthe height of the present stand 19 a is corresponding to the height ofthe conductive section 130. For example, the lowest portion of theconductive section 130 can be connected to the top of the stand 19 a sothat the overall shape of the LED filament 100 is not easily deformed.In various embodiments, the conductive sections 130 may be connected tothe stand 19 a through the perforation of the top of the stand 19 a, orthe conductive sections 130 may be glued to the top of the stand 19 a toconnect with each other, but are not limited thereto. In an embodiment,the conductive section 130 and the stand 19 a may be connected by aguide wire, for example, a guide wire connected to the conductivesection 130 is drawn at the top of the stand 19 a.

As shown in FIG. 5B, in the present embodiment, the height of theconductive section 130 is higher than the two conductive electrodes 110,112 in the Z direction, and the two LED sections 102, 104 arerespectively shaped upward from the two conductive electrodes 110, 112to the highest point and then are bent down to connect with theconductive section 130. As shown in FIG. 5C, in the present embodiment,the contour of the LED filament 100 in the XZ plane is similar to the Vletter, that is, the two LED sections 102, 104 are respectively shapedobliquely upward and outward and are bent respectively at the highestpoint and then obliquely inwardly to connect with the conductive section130. As shown in FIG. 5D, in the present embodiment, the LED filament100 has a contour in the shape like S letter in the XY plane. As shownin FIG. 5B and FIG. 5D, in the present embodiment, the conductivesection 130 is located between the conductive electrodes 110, 112. Asshown in FIG. 5D, in the XY plane, the main bending points of the LEDsections 102, 104, and the conductive electrodes 110, 112 aresubstantially on the circumference centered on the conductive section130.

In sum, according to the abovementioned embodiments, the description hasclearly disclosed a strip of filament with multiple dimming control bytwo LED sections. According to the description, a person having ordinaryskill in the art can easily implements a strip of filament with multipledimming control by two or more LED sections.

The invention has been described above in terms of the embodiments, andit should be understood by those skilled in the art that the presentinvention is not intended to limit the scope of the invention. It shouldbe noted that variations and permutations equivalent to those of theembodiments are intended to be within the scope of the presentinvention. Therefore, the scope of the invention is defined by the scopeof the appended claims.

What is claimed is:
 1. An LED light bulb, comprising: a lamp housing,doped with a golden yellow material or coated with a yellow film on itssurface, a bulb base, connected with the lamp housing, a stem with astand extending to a center of the lamp housing, disposed in the lamphousing, a LED filament disposed in the lamp housing, at least a half ofthe LED filament is around a center axle of the LED light bulb, wherethe center axle of the LED light bulb is coaxial with a axle of thestand, and the LED filament comprising: a plurality of LED sectionsincluding at least two LED chips electrically connected to each otherthrough a wire, at least one conductive sections located betweenadjacent LED sections, and a light conversion layer with at least a toplayer and a base layer opposite to the top layer of the light conversionlayer, disposed on at least one side of the LED chips; two conductivesupports, connected with the stem and the LED filament; a drivingcircuit, electrically connected with both the conductive supports andthe bulb base; a plurality of supporting arms, each of the supportingarms comprises a first end and a second end, where the first end of eachof the supporting arms is connected with the stand of the stem while thesecond end of each of the supporting arms is connected with the LEDfilament; wherein the base layer of the light conversion layer is formedfrom organosilicon-modified polyimide resin composition comprising anorganosilicon-modified polyimide and a thermal curing agent, wherein theorganosilicon-modified polyimide comprises a repeating unit representedby the following general formula (I):

wherein Ar¹ is a tetra-valent organic group having a benzene ring or analicyclic hydrocarbon structure, Ar² is a di-valent organic group havinga monocyclic alicyclic hydrocarbon structure, R is each independentlymethyl or phenyl, n is 1:5; wherein the organosilicon-modified polyimidehas a number average molecular weight of 5000˜100000; and wherein thethermal curing agent is selected from the group consisting of epoxyresin, isocyanate and bisoxazoline compounds, wherein the base layer ofthe light conversion layer comprise an upper surface where the LED chipsis positioned on and a lower surface opposite to the upper surface ofthe base layer, the upper surface of the base layer having a first areaand a second area, where the surface roughness of the first area is lessthan that of the second area with a cell; and wherein the lower surfaceof the base layer comprises a third area having a surface roughnesswhich is higher than that of the first area of the upper surface.
 2. Thelight bulb of claim 1, wherein the conductive section includes aconductor connecting with the LED section.
 3. The light bulb of claim 2,wherein the length of the wire connecting between the LED chips is lessthan the length of the conductor.
 4. The light bulb of claim 3, whereinthe shortest distance between the two LED chips respectively located inthe two adjacent LED sections is greater than the distance between twoadjacent LED chips within one of the LED sections.
 5. The light bulb ofclaim 4, wherein the length of the conductive section is greater thanthe distance between two adjacent LED chips in one single LED sections.6. The light bulb of claim 5, wherein Ar¹ is a tetra-valent organicgroup having a monocyclic alicyclic hydrocarbon structure or abridged-ring alicyclic hydrocarbon structure.
 7. The light bulb of claim6, wherein Ar² is a di-valent organic group comprising a functionalgroup having active hydrogen, where the functional group having activehydrogen is any one of hydroxyl, amino, carboxy and mercapto.
 8. Thelight bulb of claim 7, wherein Ar¹ is derived from a dianhydride, andAr² is derived from a diamine.
 9. The light bulb of claim 8, wherein theorganosilicon-modified polyimide resin composition further comprises anadditive selected from the group consisting of fluorescent powders, heatdispersing particles and a coupling agent.
 10. The light bulb of claim9, wherein the organosilicon-modified polyimide composition has arefractive index of 1.4:1.55.
 11. The light bulb of claim 10, whereinthe organosilicon-modified polyimide resin composition is prepared byvacuum defoaming, the vacuum used in the vacuum defoaming is −0.5-0.09MPa.
 12. The light bulb of claim 11, wherein the base layer having anelongation at break of 1:5%.
 13. The light bulb of claim 12, wherein theorganosilicon-modified polyimide resin composition have thermalconductivity more than 1.65 under the condition of adding small particlesize of below 1 μm, medium particle size of 1:30 μm and large particlesize of above 30 μm.
 14. The light bulb of claim 13, wherein the amountof the coupling agent=(the amount of the heat dispersing particles* thespecific surface area of the heat dispersing particles)/ the minimumcoating area of the coupling agent.
 15. The light bulb of claim 13,wherein a Cartesian coordinate system having an x-axis, a y-axis and az-axis is oriented for the LED light bulb where the z-axis is parallelto the stem of the LED light bulb, the number of LED section is two, thebending points of each of the LED sections are at the same height in thez-direction.
 16. The light bulb of claim 15, wherein the degree of thebending of the conductive section is the same as or greater than thedegree of the bending of the LED sections.
 17. The light bulb of claim16, wherein the height of the stand is corresponding to the height ofthe conductive section.
 18. The light bulb of claim 17, wherein thebending points of the LED sections and the conductive electrodes aresubstantially on the circumference centered on the conductive section inthe XY plane which is perpendicular to the z-axis.
 19. The light bulb ofclaim 18, wherein each of the LED sections respectively have a circulararc at the highest point of the LED filament in the z-direction.
 20. TheLED light bulb according to claim 19, wherein points of the LED filamentin an xyz coordinates are defined as X, Y, and Z and satisfy a curveequation, an origin of xyz coordinates is at the stem top, an x-y planeof the xyz coordinates passes through the stem top and is perpendicularto the height direction, a z-axis of xyz coordinates is coaxial withstem, and the two conductive electrodes are symmetrically disposed attwo sides of a y-axis of the xyz coordinates, the curve equation is:X=m1*cos(t*360),Y=m2*sin(t*360),Z=n*cos(t*360*k), wherein, t is a variable between 0 and 1, the LEDfilament varies along an x-direction, a y-direction, and a z-directionaccording to t; wherein, when X=0, a max value of |Y| is m2, and a maxvalue of IZI is n; wherein, when Y=0, a max value of |X| is m1, and amax value of |Z| is n; wherein, when Z=0, a max value of |X| is m1, anda max value of |Y| is m2; wherein m1 is a length in the x-direction, m2is a length in the y-direction, n is a height of the highest point fromthe x-y plane in the z-direction, and k is a number of the highestpoint.